Sharp-edge deflection



1941- K. SCHLESINGER 2,252,441

SHARP-EDGE DEFLECTION Filed April 722, 1938 5 Sheets-Sheet 1 def/ecfedJnvenfop:

1941- K. SCHLESXNGER 2,252,441

SHARP-EDGE DEFLECTION Filed April 22, 1938 3 Sheets-Sheet 2 Fig 5Jnvemop:

Mull/w 1941- K. SCHLESINGER 2,252,441

SHARP-EDGE DEFLECTION Filed April 22, 1938 Y 3 Sheets-Sheet 3 VOL 7/] GEIVE Fig. 7

JnVen fon- Patented Aug. 12, 1941 SHARP-EDGE DEFLECTION KurtSchlesinger, Berlin,

Radioaktiengesellschaft D.

Germany, assignor to S. Loewe, Berlin- Steglitz, Germany, a company ofGermany 1938, Serial No. 203,487

Application April 22,

In Germany April 26,

7 Claims.

The present invention relates to cathode ray tube arrangements, moreparticularly for television purposes wherein means comprising at leastone pair of deflecting plates are provided for deflecting the cathoderay in two directions perpendicular to one another.

It is known that a large bundle of rays which, when not deflected, isfocussed sharply on the screen will not give a sharp image point in thecase of deflection beyond a critical angle. It is also known that thiscritical angle can be increased if the two plates are supplied withreverse phase deflecting voltages so that their potentials oscillatesymmetrically with respect to the anode potential. New investigations,however, have shown that even in this case an enlargement of the imagepoint takes place if the beam is deflected beyond an angle of about 17.For several reasons, however, it is desirable to have considerablygreater deflections of the ray with full sharpness of Then can beobtained either larger pictures with a given length of tube or shortertubes with a given size of picture. In the latter case it is alsopossible, for electron optical reasons, to obtain a smaller image pointand a greater density of light.

It is. an object 'of the present invention to perform a widean'gle'defiection in cathode ray tubes, more particularly for televisionpurposes, and at the same time to maintain an irreproachable sharpnessof the picture over its entire area.

According to the invention, in a cathode ray tube arrangement of theabove mentioned type, wherein the cathode ray tube comprises an anodewhich is mounted immediately adjacent to the deflecting plates at theirside facing the cathode and is connected to a source of constantpotential, and there are provided means for producing the effect of acommon bias applied to the deflecting plates, which is positive withrespect to the anode and varies in rhythm with the deflecting voltagebuilt up across the deflecting plates, the peak value of the common biasbeing preferably substantially equal to one half of the peak value ofthe deflecting voltage.

The invention will be better understood with the aid of, and furtherfeatures of the invention will be apparent from the following moredetailed description and the accompanying drawings in which- Fig. 1illustrates an experimental circuit used for obtaining the eflects shownby Figs. 2a and 2b,

Figs. 3, 4, 5, '7, and 8, in a purely diagrammatic fashion and by way ofexample, illustrate cirthe edges of the picture.

cuits for avoiding the effect according to Fig. 2a, whilst Fig. 6 is agraph showing age and an example of a common to the deflecting plates.

The following experiment illustrated by Fig. 1 has been made forinvestigating the errors of an electro-static deflecting system:

In a cathode ray tube there are provided two deflecting plates 1 and 2beyond an anode 3.

the deflecting voltbias applied The bundle of cathode rays 4, inthenon-deflected condition, is 'focussed sharply on to the screen 5. Thebattery '6 supplies to the plates the deflecting potential. In theexampleshown the ray is thus deflected downwards. In parallel with thebattery 6 there is connected a potentiometer I, the wiping contact ofwhich is connected with the anode 3. If a certain deflection isadjusted, it can be ascertained that beyond the critical angle ofdeflection the sharpness of the point "is maintained in full if plate I,which is connected to the negative terminal of the battery, is at thesame time connected to the anode and the positive plate exhibits inrelation to the ray the full deflecting potential. In Fig. 1 thisconnection is obtained by displacing the wiper of the potentiometertowards the right. If the opposite adjustment is made,i. e., thepositive plate connected to the anode and the negative plate allowed tooscillate in relation to the ray, the sharpness of the edge of thepicture will be considerably poorer.

Further detailed investigations have shown that not a marginal field nora variation of the speed of the ray, but probably a space charge effectis causing the described eiiect.

In Fig. 2a there is shown the wrong connection, the anode 3 beingconnected with'the positive plate 2, and in Fig. 2b the properconnection. In Fig. 2a the point of intersection of the single raysisdisplaced from the plane of the screen 5 towards the anode to thepoint 511. The focal distance of the system is shortened and the imageloses its sharpness at the edge.

In "the proper connection, Fig. 2b, the anode being connected with thenegative plate, the reverse effect occurs. The rays nearer the positiveplate are deflected somewhat more strongly than those opposite to thenegative plate. The focal distance of the system is extended from 5a to5b. The image point remains on the screen.

It has been found that any variation of the sharpness of the image pointduring the whole deflectionperiod can be avoided when both plates arefurnished, in addition to the deflectingpotentials, with a commonvarying bias increasing with the absolute value of the deflectingvoltage in such a way that the potential of the deflecting plates isalways higher than or at least equal to the potential of the anode. Itwill be understood from the following that the desired effect, i. e.,the effect of a common bias applied to the deflecting plates, can alsobe obtained by circuit means which do not supply the deflecting plateswith a common bias in the strict sense of the word.

The simplest way to realize the desired effect is to provide meansconnecting that deflecting plate which is instantaneously negative withthe anode. That means that the connection between plates and anode mustbe commutated twice in a complete deflection period from the left to theright and back when push-pull deflection is used. As regards thetechnical reduction to practice the following circuit illustrated byFig. 3 would be conceivable in principle:

The two plates I and 2 are connected with the secondary of a deflectiontransformer 8 the primary of which is fed by a relaxation oscillator 23.The mean point of the secondary is connected by way of a leak resistance9 with the anode 3, Two rectiflers I (la, lfib (diodes are shown in thedrawings) are connected by the cathodewith the plates and by the anodeswith the tube anode 3. Neither of the plates is then able: to becomenegative in relation to the tube anode, whereas the potential of theinstantaneously positive plate is able to oscillate with respect to theanode without obstruction.

Consequently each plate carries alternately constant anode potential forone half period of deflection and a positive saw-tooth potential for thenext half period, the potentials of both plates having 'a phasedifference of one half period. Thus the voltage between both plates hasa sawtooth wave form the amplitude of which can easily be made equal tothe required deflecting voltage. The efiect is exactly the same as ifthe plates were oscillating in push-pull and both plates had a commonpositive bias increasing with the absolute value of the deflection. Thisresults from the fact that the mean potential of the deflectingcondenser varies proportional to and with the same frequency as theabsolute value of the potential difference produced by the reverse phasevoltages which would appear at the terminals of the secondary winding oftransformer 8, if ordinary push-pull operation were used.

The problem can also be solved in a similar way by means of gridcontrolled thermionic tubes according to Fig. 4. Two amplifying tubes l9and I 9' are via condensers 20 and 20 coupled with the two deflectingplates I and 2. 32 is the common anode battery of the tubes, 33 and 33'are the anode resistances. The grids of the tubes are provided with gridcurrent limiting resistances 2| and 2| and have no bias voltage. Thusthe tubes work as class B-amplifiers and produce exactly the desireddeflection voltages. Instead of utilizing the grid currents for cuttingoff the undesired exciting half-wave a special pair of rectiflers, forexampletwo crystal detectors, can naturally also be included on thesecondary side of 8, i. -e., in front of the grids of the tubes. inwhich case the tubes, as normal class A-amplifiers, would then have apurely amplifying function to perform.

A disadvantage of this circuit is that associated with all classB-ampliflers consisting in the fact that in the vicinity of the zeropoint of deflection there is a departure from the linearity, which canonly be avoided with difficulty by careful biassing and the selection ofequal tubes. This comparatively harmless zero anomaly in the case ofsound amplifiers can be intolerable in television.

The circuit system shown diagrammatically in Fig. 5 and more detailed inFig. 7 is free of this disadvantage. The deflecting plates are againconnected with the secondary 8 of a relaxation transformer the meanpoint of which, however, is not, as usual connected with the anode 3directly, a variable bias 1) being included between. The additionalvoltage 22 must be approximately one-half of the deflecting voltage andtraverse a positive maximum twice during one relaxation period.

In Fig. 6 there have been entered the courses of the deflecting voltage(2 and the additional voltage 12. As measurements have shown, the courseof 21 requires to be represented, at least in the case of a spherical orplane screen, not by a straight, but by a parabolic curve in order toobtain the best compensation. This fact enables the potential 22 to beproduced without the use of rectifying tubes simply by integration of alinear relaxation curve, e. g., by charging a second condenser via arather high resistance by the voltage of a usual relaxation condenser.

In Fig. '7 there is shown an embodiment of the scheme according to Fig.5. I6 is the relaxation condenser charged via resistance [1 anddischarged by the grid controlled thermionic tube It). The condenser iscoupled to an amplifying tube IS the anode circuit of which contains inseries the primary coils of the transformers 8 and I2. The transformer 8for the deflecting voltage at is shunted on the primary side by arelatively low resistance H in order to enable it to yield on itssecondary terminals a linear relaxation voltage. The secondary of 8should have a self-induction which is so small that the natural periodof the secondary circuit comprising the deflecting plates and the leadsto them is equal to or preferably smaller than the return period of theray. The transformerl2 for the voltage U is tuned considerably lowerthan the transformer 8. It has preferably on the primary and secondaryside two to three times more windings than 8 and is, like 8, shunted onits primary side by a resistance l3. The exact adjustment of the voltage11 takes place by varying experimentally the capacity of the integratingcondenser !4 or the charging resistance 34. In the case of a 4G0-lineimage it amounts to approximately 300 m. The voltage arising at thesecondary terminals of I2 is already the desired parabolic voltage '1).(The same effect can naturally also be obtained by employing on theprimary side a larger condenser.) The secondary terminals of I2 areconnected to the anode 3 respectively via a damping resistance 24 ofapproximately '10 to 10 ohms to the mean point of the secondary of 8 inorder to prevent an oscillation of the circuit l3--2 initiated by thereturn beat and otherwise disturbing the linearity of the deflection.

To enable the transformers 8 and J2 to function independently of eachother the tube l5 must be a pentode, 'as otherwise the anode currentwould be affected by the variable impedances of the transformers andwould not be an undistorted reproduction of the purely linear relaxa-*tion potential :resulting cat the storage condens- "81' 1| 6.

Thearrangement described above can be em- .ployedi-alsoin-the case ofelectrostatic deflection in .both coordinates.

Mixed deflection, however, hasalsobeen found particularly suitable, theslow As comparedwith thetmethod of performing rapid .deflectionsmagnetically, the method according to the invention has .the advantageof requiring aconsiderably.smallerpower input. It'has been carried outup to .angles of approximately 2 25 without any limit having beenreached.

The effect of the positive bias of the plates is only suflicient aloneif the spacing of the plates does not exceed the thickness of thecrosssection of the ray when entering the plates. Even greater angles ofdeflection can, however, be obtained if, together with the plates, theelectronic lens is also controlled by the rectifying potential or by apart of the same in such fashion that the refractive power of thereproducing lens decreases when the angle of deflection increases. Thiscan be performed in the case of both magnetic as Well as electriclenses.

A circuit system for combined plate and lens control is shown in Fig. 8.The linear relaxation potential 23 is amplified by a screening gridtube, preferably a pentode l5. The anode current flows in series throughthe deflecting transformer 8, which is shunted by the resistance II, The

anode current then traverses a part of the poten-' tiometer 35 the wholeresistance of which remains in parallel to the primary of thetransformer l2 so that its excitation is able to be adjusted by theslider of 35. By means of the condenser I4 the secondary voltage of I2is integrated, as described above. At the potentiometer 28 a suitablepart-potential, which can be adjusted by observing the effect at theimage field, is tapped and is passed via condenser 21 to the lenselectrode 26. The lens in this case is shown as an electro-static one.It is furnished via the high resistance 29 with a bias by a tapping onthe potentiometer 30 shunting the anode battery 3|. This bias is sochosen that the centre of th picture is sharp.

I claim:

1. In a cathode ray tube arrangement comprising means including acathode for producing a cathode ray, a screen, means including an anodefor focusing said cathode ray on said screen, and means including a pairof deflecting plates for deflecting said cathode ray, said anode beingmounted immediately adjacent to said deflecting means at their sidefacing said cathode and being connected to a source of constant anodepotential: means for producing the effect of a common, variable positivebias applied to said deflecting plates with respect to said anode andincreasing with the absolute value of the deflection of said cathoderay.

2. In a cathode ray tube arrangement comprising means including acathode for producing a cathode ray, a screen, means including an anodefor focusing said cathode ray on said screen, and means including a pairof deflecting plates for deflecting said cathode ray, said anode beingmounted immediately adjacent to said deflecting means at their sidefacing said cathode and being connected to a source of constant anodepotential: means for producing the effect of a com- .mon, variable.positive bias applied -to-said deflectingzplateswith respect to said"anode andincreasing with'the absolute value of the deflection of;sa'id"cathode :ray, said last mentioned means comprising "a circuitconnecting the instantaneously negativeof said plates to said anode.

3; In a cathode ray tube arrangement comprising means including acathode for producing a cathode ray, a screen, means including an anodefor focusing said cathode ray on said screen, means including a pair ofdeflecting plates for deflecting said cathode ray, said anode beingmounted immediately adjacent to said deflectingzmeans at their sidefacing said cathode and being connected to a source of constant anodepotential, and a deflecting voltage transformer the secondary winding ofwhich is "connected to said deflecting plates: a circuit additionallyconnecting each of said plates via a rectifier to said anode so that theinstantaneously negative of said plates is raised to anode potential.

In a cathode ray tube arrangement comprising means including a cathodefor producing a cathode ray, a screen, means including an anode forfocusing said cathode ray on said screen, means including a pair ofdeflecting plates for deflecting said cathode ray, said anode beingmounted immediately adjacent to said deflecting means at their sidefacing said cathode and being connected to a source of constant anodepotential, and a deflecting voltage transformer: a circuit comprisingtwo leakage resistances each connecting one of said plates to saidanode, and two thermionic tubes each being provided with cathode,control grid, anode, a high grid resistance and an anode resistance, thecathodes of said thermionic tubes being connected to the mean point ofthe secondary of sa d deflection transformer, said grids via said gridresistance to th terminals of said secondary, and the anodes of saidthermionic tubes each to one of said plates.

5. In a cathode ray tube arrangement comprising means including acathode for producing a cathode ray, a screen, means including an anodefor focusing said cathode ray on said screen, means including a pair ofdeflecting plates for deflecting said cathode ray, said anode beingmounted immediately adjacent to said deflecting means at their sidefacing said cathode and being connected to a source of constant anodepotential, and means for connecting said deflecting plates with arelaxation generator adapted to produce reverse phase deflectingpotentials symmetrical to the potential of said anode: means forproducing the effect of a common bias applied to said deflecting plates,which is positive with respect to said anode and varies in rhythm withthe deflecting voltage built up across said deflecting plates, the peakvalue of said bias being substantially equal to one half of the peakvalue of said deflecting voltage.

6. In a cathode ray tube arrangement comprising means including acathode for producing a cathode ray, a screen, means including an anodefor focusing said cathode ray on said screen, means including a pair ofdeflecting plates for deflecting said cathode ray, said anode beingmounted immediately adjacent to said deflecting means at their sidefacing said cathode and being connected to a source of constant anode Dtial, and means for connecting said deflecting plates with a relaxationgenerator adapted to produce reverse phase deflecting potentialsmetrical to the potential of said anode: means for producing the effectofa common bias of linear wave form applied to said deflecting plates,which is positive with respect to said anode and varies in rhythm withthe deflecting voltage built up across said deflecting plates, the peakvalue of said bias being substantially equal to one-half of the peakvalue of said deflecting voltage.

'7. In a cathode ray tube arrangement comprising means including acathode for producing a cathode ray, a screen, means including an anodefor focusing said cathode ray on said screen, means including a pair ofdeflecting and being connected to a source of constant anode potential,and means for connecting said deflecting plates with a relaxationgenerator adapted to produce reverse phase deflecting potentialssymmetrical to the potential of said anode: means for producing theefiect of a common bias of linear wave form applied to said deflectingplates, which is positive with respect to said anode and varies inrhythm with the deflecting voltage built up across said deflectingplates, the peak value of said bias being substantially equal toone-half of the peak value of said deflecting voltage, said lastmentioned means consisting of a circuit adapted to suppress the platesfor deflecting said cathode ray, said anode 5 actually negative wave ofsaid deflecting voltage.

being mounted immediately adjacent to said deflecting means at theirside facing said cathode KURT SCHLESINGER.

